One apparatus for sealing a well is the BOP. The BOP is a safety mechanism that is used at a wellhead of an oil or gas well. The BOP may be used for offshore drilling and also for land-based drilling. The BOP is configured to shut the flow from the well when certain events occur. One such event may be the uncontrolled flow of gas, oil or other well fluids from an underground formation into the well. Such event is sometimes referred to as a “kick” or a “blowout” and may occur when formation pressure exceeds the pressure generated by the column of drilling fluid. This event is unforeseeable and if no measures are taken to prevent and/or control it, the well and/or the associated equipment may be damaged.
The BOP may be installed on top of the well to seal the well in case that one of the above events is threatening the integrity of the well. One type of BOP, an annular BOP, is conventionally implemented as a valve to release the pressure either in the annular space between a casing and a drill pipe or in the open hole (i.e., hole with no casing) during drilling or completion operations. Another type of BOP, a ram BOP, can be located below the annular BOP and above the wellhead. These ram BOPs can generally be broken down into a few categories: (1) blind rams for sealing an open hole, (2) pipe rams for sealing a hole with drill pipe in use, (3) shear rams for sealing the hole and cutting the drill pipe, etc.
FIG. 1 shows a well 10 located in an offshore environment. A wellhead 12 of the well 10 may be fixed to the seabed 14. A ram BOP 16 is secured to the wellhead 12. FIG. 1 shows, for clarity, the BOP 16 detached from the wellhead 12. However, the BOP 16 is attached to the wellhead 12 or another part of the well 10. A drill pipe 18 is shown traversing the ram BOP 16 and entering the well 10. The ram BOP 16 may have two ram blocks 20 attached to corresponding pistons 22. The pistons move integrally with the ram blocks 20 along directions A and B to close the well.
A cut view of the ram BOP 16 that shows the ram blocks 20 is shown in FIG. 2. The ram blocks 20 are shown closed inside a cavity 24. The cavity 24 may be bordered, at one end, by a top seat 26 and a wear plate 28. The ram blocks 20 may include a packer 30 (which may be an elastomer) and a top seal 31, which seals the well 10 when the ram blocks 20 are closed.
In situations when the ram BOP is a pipe ram BOP used for shearing the drill pipe or other tools in the hole when sealing the well, having the desired shear strength and shared load through the desired load bearing surfaces is desired. This can be complicated by variable forces acting upon the system, such as, the reaction force produced by the drill line when asymmetrically disposed relative to the shear surface of the ram block 20, and force produced by variable upward pressure from the kick or additional items inside of the drill pipe that also need to be sheared off to seal the well, e.g., a cable attached to a down hole piece of equipment, to name just a few examples.
In addition, piston 22 may neck down into a piston rod portion 302 which includes a neck section 304 and head section 306 as shown in FIG. 3. In FIG. 3, a portion of the piston rod 302 is shown as dashed lines representing the portion of the piston rod 302 which is covered by the ram block 20 when looking from the top down. The piston rod head section 306 has a face 308 which is in contact with the ram block 20. This contact surface of the face 308 is where the force is applied from the piston 22 to the ram block 20 when closing the BOP to shear, for example, a load 314. Also shown is a gap 310 which exists between the piston rod 302 and the ram block 20 when the ram block 20 is installed. Since there is a gap 310, shoulders 312 of the piston rod 302 are not applying force from the piston rod 302 to the ram block 20. Additionally, this gap may allow undesirable twisting forces to be exerted upon the piston rod neck 304. For example, if the load 314 is asymmetrically distributed relative to the ram block 20, as shown in FIG. 3, a non-uniform force would act on head section 306, which in turn will try to bend the neck section 304 along direction A.
Accordingly, it would be desirable to provide systems and methods that can achieve the sealing of a well and shear materials in the well but also avoid the additional challenges described above.